The present invention relates to a magnetic transducer which employs a magnetoresistive element, and more particularly to a structure which is well suited to apply a transverse biasing magnetic field to a magnetoresistive element.
A magnetoresistive element (hereinbelow, written "MR element") exploits the fact that the resistance R of the MR element is varied by a magnetic field H to which the MR element is subjected. As shown in FIG. 1, the resistance variation is a nonlinear variation. Accordingly, in order to construct a magnetic transducer of high efficiency by detecting the nonlinear resistance variation, the operating point of the MR element needs to be shifted to point B indicated in FIG. 1, that is, a magnetic field H.sub.b needs to be applied beforehand, thereby to improve the linearity of the resistance variation of the MR element and to enhance the sensitivity of the element. The magnetic field H.sub.b applied in advance is called the "transverse biasing magnetic field".
As expedients for applying the transverse biasing magnetic field to the MR element, there have been proposed various methods, for example, one wherein as disclosed in the official gazette of Japanese Patent Application Laying-open No. 49-74522 or No. 49-74523, currents are caused to flow through both a magnetoresistive film (hereinbelow, written "MR film") and a conductive film which is disposed in close contact and electrical contact with the MR film, and a magnetic field generated by the current flowing through the conductive film is used as the transverse biasing magnetic field, and one wherein as disclosed in the official gazette of Japanese Patent Application Laying-open No. 50-1712, a hard magnetic film is arranged in proximity to an MR film, and a magnetic field generated by the residual magnetization of the hard magnetic film is used as the transverse biasing magnetic field.
With those methods of the prior arts which have been disclosed in the official gazettes of Japanese Patent Application Laying-open Nos. 49-74522 and 49-74523, in order to attain a sufficient bias field strength, the resistance of the conductive film needs to be rendered lower than that of the MR film thereby to permit a great current to flow. For this reason, the resistance variation of the MR film is short-circuited by the conductive film, and it has been impossible to expect a great output in case of constructing a magnetic transducer.
In the prior arts, no regard has been paid to the difficulty that the bias field strength changes due to changes in the height of the MR film and the height of the conductive film or the hard magnetic film for generating the transverse biasing magnetic field, so the output and linearity of a magnetic transducer change. In case of constructing the magnetic transducers with these prior arts, therefore, the heights of the MR film and the conductive film or hard magnetic film for applying the transverse biasing magnetic field need to be held at high precision. Another problem is that, when the magnetic transducer reproduces a signal in contact with a magnetic recording medium, the film height changes due to wear, and the film height change incurs degradation in the linearity, so the magnetic transducer fails to operate normally.
The following references are cited to show the state of the art; (i) Official Gazette of Japanese Patent Application Laying-open No. 49-74522, corresponding to U.S. Pat. No. 3,814,863; (ii) Official Gazette of Japanese Patent Application Laying-open No. 49-74523, corresponding to U.S. Pat. No. 3,840,898; (iii) Official Gazette of Japanese Patent Application Laying-open No. 50-1712, corresponding to U.S. Pat. No. 3,813,692.